code: def test_is_in_null_series() -> None:
      df = pl.DataFrame({"a": ["a", "b", None]})
      result = df.select(pl.col("a").is_in([None]))
      expected = pl.DataFrame({"a": [False, False, None]})
      assert_frame_equal(result, expected)
  
imports: from __future__ import annotations
  from datetime import date
  import pytest
  import polars
  from polars import StringCache
  from polars.testing import assert_frame_equal, assert_series_equal
label_desc: Use image node_id 16 for calling a global function with example usage: test_is_in_null_series() without return types